A) Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display capable of providing a high contrast ratio by using a monochromatic light source.
B) Description of the Related Art
A super-twisted nematic (STN) liquid crystal display (LCD) has been used as a liquid crystal display device of a high duty ratio. One type of STN-LCD is a blue color mode display device. A so-called blue color display, in which blue color is presented when a voltage is not applied and white color is presented when a voltage is applied can be made by disposing a polarizing axis of an analyzer at 30 degrees in a counter-clockwise direction relative to long axes of liquid crystal molecules on light emitting (optical output) side and by disposing a polarizing axis of a polarizer at 30 degrees in a clockwise direction relative to long axes of liquid crystal molecules on light incident (optical input) side.
JP-A-2004-62021 proposes to improve light shielding performance in a cut-off state by mixing dichromatic pigment in liquid crystal composition of STN-LCD of the blue color mode. A compensation plate or plates may be used as another means for improving light shielding performance.
The blue color mode generally uses a white color back light. If a monochromatic light source such as a light emitting diode (LED) is used, it is possible to provide a normally black mode in which a back light color becomes a display color in black background, in which a transmission factor is lowered in the absence of applied voltage, and is increased to a level suitable for display in the presence of applied voltage at an emission wavelength of the back light.